Assembled camshafts are known, for example from WO2008/075094, GB 2424258 and EP 1362986, which comprise an inner shaft and an outer tube that are rotatable relative to one another. A first set of cams is secured for rotation with the outer tube while a second set of cams is rotatably mounted on the outer tube and is connected for rotation with the inner shaft by way of pins that pass with clearance through circumferentially elongated slots in the outer tube. Such a camshaft, which allows the relative phase of cams rotatable about a common axis to be changed, is referred to herein as an SCP camshaft.
There are also known hydraulically operated vane-type cam phasers that are intended to drive an SCP camshaft, an example of such is a phaser as disclosed in U.S. Pat. No. 6,725,817. Such phasers will herein be referred to as twin phasers, because they have two output members, one for driving the inner shaft of the SCP camshaft and the other for driving its outer tube. The phase of both of the output members are adjustable hydraulically relative to the engine crankshaft, such as by controlling the flow of oil under pressure to arcuate working chambers arranged on opposite sides of radial vanes connected to a respective one of the output members. This could equally be achieved with two single phasers arranged in series or parallel, attached to the front of the SCP camshaft.
A known SCP camshaft and twin phaser assembly based on the disclosure of WO2008/075094 and believed to represent the closest prior art will now be described with reference to the accompanying FIGS. 1 and 2, in which FIG. 1 shows an exploded view of the twin phaser and the front end of the camshaft while FIG. 2 shows an axial view through the twin phaser when assembled on the camshaft.
In the twin phaser 10 of FIGS. 1 and 2, the phase of each of two output members, formed as end plates 14, 16, is adjustable relative to the engine crankshaft. The phaser has a stator 12 formed as a gear 20 to be driven by the engine crankshaft. If the phaser is chain driven, the gear 20 would be replaced by a sprocket. The stator 12 is annular and has six arcuate recesses 13. Three of the recesses receive vanes 15 projecting from the front end plate 14 and the other three receive vanes 17 projecting from the rear end plate 16.
The camshaft 30 terminates within a front bearing 24 which is formed with three screw threaded holes receiving ring dowels 23 and is fast in rotation with the outer tube 26 of the camshaft 30.
The twin phaser 10 is supported on a bearing support 50 which comprises a ring with three axially projecting hollow legs 54. The ring 50 is engaged in use by an oil feed spigot that projects from a cover overlying the front end of the engine block. The front cover may, for example, be an adaptation of that described in GB-A-2,329,675. The stator 12 of the twin phaser is in turn supported by the radially outer surface of the support bearing 50 and can rotate through only a few degrees relative to it. Various passageways and oil grooves in the support bearing 50 allow oil from the engine front cover to be supplied under pressure to the working chambers of the twin phaser 10.
The legs 54 of the support bearing 50 pass through three arcuate clearance slots 19 formed in the rear end plate 16 to contact the axial end face of the bearing 24 that is mounted on the outer tube 26 of the SCP camshaft 30. The bearing support 50 is axially clamped between the front plate 14 of the twin phaser 10 and the bearing 24 by means of three bolts 31 which pass through the hollow legs 54 and clamp the front end plate 14, the support bearing 50 and the bearing 24 to one another. This ensures that the front end plate 14 is fixed both axially and rotationally in relation to the outer tube 26 of the SCP camshaft 30.
Additionally, the hollow legs 54 of the support bearing 50 are aligned in relation to the bearing 24 by means of the ring dowels 23 that project from the axial end surface of the bearing 24 into the hollow legs 54 of the support bearing 50.
The rear end plate of the twin phaser 10 is directly secured onto the inner shaft 40 of the SCP camshaft 30 by means of a bolt 41 that is screw threaded into a bore in the axial end face of the inner shaft 40.
In the above described assembly, the two output members of the twin phaser are arranged one at the front, namely the end plate 14, and the other at the rear, namely the end plate 16. In an internal combustion engine, it is necessary to sense the angular position of these output members so that the electronic engine control unit (ECU) can correctly control camshaft timing.
Though not specifically described in WO2008/075094, the front and rear output members produced by the present Applicants did in practice have timing features on them, for triggering adjacently mounted sensors. In FIG. 1, the timing feature on the front plate 14 comprises four axially projecting teeth 60 and that on the rear plate comprises four radially projecting teeth 62. The sensors need to be positioned next to these timing features in such a way that electrical sensor signals are generated, which can be used by the ECU to control the phaser 10.